1. Field of the Invention
The present invention relates to a self-adjusting parking brake for a motor vehicle and including a bridge girder provided with toothing, a brake lever pivotally supported on the bridge girder, a locking pawl for securing the brake lever on the bridge girder in any arbitrary put-on position of the parking brake, a brake cable driving element likewise supported on the bridge girder, an adjusting spring for biasing the brake cable driving element in a rotational direction, and a spring-biased clutch for connecting the brake lever with the brake cable driving element.
2. Description of the Prior Art
Conventional self-adjusting parking brakes of the type described above are characterized in that the brake cable, which leads to the wheel brake members, is connected to a disc segment with a circumferential toothing and which forms an adjusting disc. The adjusting disc is supported on a common axle with the brake lever for rotation independently of the brake lever. The adjusting disc is biased in a rotational direction by an adjusting spring formed as a spiral spring. The adjusting disc is connected with the brake lever by a gripping pawl biased by a spring, in particular by a leg spring, in the engagement direction. The gripping pawl engages, upon application of the brake and thereby the pivotal movement of the brake lever from its release position into its engagement position, the toothed adjusting disc, thereby drivingly acting on the brake. The gripping pawl (see, e.g., European Publication EP-0 535 131) is formed as a rocking lever having one of its arms cooperating with the adjusting disc-forming disc segment and another of its arm cooperating with a release abutment fixedly arranged on the bridge girder which is secured to a motor vehicle body. The rocking lever acts so that in a completely release position of the brake lever, the brake lever is disengaged from the adjusting disc, with the adjusting disc being exclusively under the influence of its biasing spring.
These and similar self-adjusting parking brakes are primarily characterized in that the coupling of the brake lever with a cable pulley or a similar driving element for at least one brake cable is effected with a ratchet element, in particular, with a spring-biased pawl. This inevitably generates noise upon actuation of the parking brake on one hand, and on the other results in relatively high manufacturing costs as only relatively small tolerances are allowed.
European Publication EP-0 162 749 discloses an adjusting device which includes a driving element formed as a one-arm lever connected with the brake cable. The one-arm lever is supported on the same carrier as the brake lever and is provided with an axially extending toothing engageable with a complementary toothing provided on a side surface of the brake lever under the action of a pressure spring. The pressure spring is so formed and arranged that is simultaneously imparts a rotational force to the driving element in the brake cable tensioning direction. As a result of the inclination of the opposing toothings of the brake lever and the driving element the rotational force applied to the driving element provides, in the release position of the brake lever, for adjusting of the driving element in case a play has developed in the brake system. The drawback of this adjusting device consists in that a single spring should provide for two different functions and, therefore, cannot be for effecting both functions. Besides, at no time, adjustment of the driving element, which is completely independent of the brake lever, can be achieved.
Accordingly, an object of the invention is to provide a self-adjusting parking brake for a motor vehicle of the above-described type in which an automatic, stepless to a most possible extent adjustment, which is completely independent of the brake lever, is effected after each actuation of the parking brake, without increase of manufacturing and assembly costs.